Dermatopathology is a joint subspecialty of dermatology and pathology and to a lesser extent of surgical pathology that focuses on the study of cutaneous diseases at a microscopic and molecular level. It also encompasses analyses of the potential causes of skin diseases at a basic level. Dermatopathologists work in close association with clinical dermatologists. In fact, most of them are trained primarily in dermatology themselves. Dermatologists can recognize most skin diseases based on their appearances, anatomic distributions, and behavior. Sometimes, however, those criteria do not allow a conclusive diagnosis to be made, and a skin biopsy is taken to be examined under the microscope or are subject to other molecular tests. That process reveals the histology of the disease and results in a specific diagnostic interpretation. In some cases, additional specialized testing needs to be performed on biopsies, including immunofluorescence, immunohistochemistry, electron microscopy, flow cytometry, and molecular-pathologic analysis. One of the greatest challenges of Dermatopathology is its scope. More than 1500 different disorders of the skin exist, including cutaneous eruptions ("rashes") and neoplasms (dermatological oncology deals with pre-cancers, such as an actinic keratosis; and cancers, including both benign masses, and malignant cancers- such as basal cell carcinoma, squamous cell carcinoma, and most dangerously, malignant melanoma).